This invention relates to a magnetic recording apparatus and a magnetic recording/reproducing apparatus, and more particularly to a magnetic recording apparatus and a magnetic recording/reproducing apparatus adapted to record or reproduce a digital signal modulated in accordance with the modulation system based on the polyphase PSK (Phase Shift Keying) such as the Offset Quadrature Differential Phase Shift Keying (OQDPSK), or the Quadrature Differential Phase Shift Keying (QDPSK), or a frequency-modulated FM audio signal at the lower (deep) layer portion of the magnetic layer of a magnetic tape, and to record or reproduce a video signal at the upper (surface )layer portion thereof.
FIG. 1 is a block diagram showing the system configuration of a magnetic recording/reproducing apparatus comprising in combination, a conventional magnetic recording unit and the reproducing system thereof. Referring to this figure, a color video signal incoming to the input terminal 41 is converted to, e.g., a frequency-division multiplex signal consisting of a low frequency band carrier chrominance signal and a frequency-modulated luminance signal. The signal thus obtained, is passed through a recording amplifier 43 and a switching circuit 44, and is then recorded onto a magnetic tape 46 by means of rotary heads 45a and 45b.
On one hand, respective audio signals of the left channel (Lch) and the right channel (Rch) incoming to the input terminals 47.sub.L and 47.sub.R, are converted to a pulse code modulated (PCM) signal and are subjected to time division-multiplexing by an A/D (analog-to-digital) converter 48 and a digital signal processing circuit 49. Then, the signal thus processed, is modulated by an OQDPSK modulator 50 in accordance with the offset quadrature differential PSK modulation system. This modulated signal is sequentially passed through a recording amplifier 51 and a switching circuit 52 and is then recorded onto the magnetic tape 46 by means of rotary heads 53a and 53b.
In this instance, on an audio track where the OQDPSK modulated digital audio signal is recorded at the lower layer portion of the magnetic layer of the magnetic tape 46 by means of rotary heads 53a and 53b, the above-mentioned frequency division-multiplex video signal is recorded at the upper layer portion of the magnetic layer while forming a video track by means of rotary heads 45a and 45b.
At the time of reproducing or playback, the frequency division-multiplex video signal reproduced from the video track by means of the rotary heads 45a and 45b is sequentially passed through the switching circuit 44 and a reproducing amplifier 54 and is then delivered to a video signal processing circuit 55, by which it is converted back to the original reproduced color video signal and is then output to the output terminal 56.
On the other hand, the digital audio signal reproduced from the audio track by means of the rotary heads 53a and 53b is sequentially passed through the switching circuit 52, a reproducing amplifier 57, a waveform equalizer 58, and an OQDPSK demodulator 59, and is then delivered to a digital signal processing circuit 60, at which it is converted to a reproduced PCM signal. Then, it is converted back to the original analog audio signal by a D/A (digital-to-analog) converter 61. Thus, a left-channel reproduced audio signal and a right-channel reproduced audio signal are separately and concurrently delivered to the output terminals 62.sub.L and 62.sub.R.
As just described above, the conventional apparatus shown in FIG. 1 is a rotary head type VTR of the lower layer recording system. This apparatus directly records an OQDPSK modulated digital audio signal at the deep layer portion of the magnetic layer of the magnetic tape 46. This recording/reproducing apparatus was already disclosed in the papers e.g., Arai et al., "A STUDY ON THE DIGITALIZATION OF AUDIO SIGNALS FOR VIDEO TAPERECORDER", International Conference on Acoustics. Speech and Signal Processing, p. 29-33, 1986. In addition, the lower layer recording technology is disclosed in U.S. Pat. No. 3,542,946.
Since the conventional apparatus shown in FIG. 1 can record/reproduce digital audio signals, advantageously resulting in high quality speech. However, recording/reproducing audio signals in FM format, which is now popular for VTRs, can not be performed by the conventional apparatus of FIG. 1, and the apparatus fails to cope with video software already distributed in the market in which only FM audio signals are prerecorded. For this reason, in the prerecorded tape industrial world, even in the case where one video software has the same content as that of another one, the video software in which digital audio signals are recorded must be also prepared independent of the video software in which FM audio signals are recorded, resulting in the requirement of much time and poor economy.